The present invention relates to an apparatus and method for controlling ink supply amount/registration adjustment in a printing press, which simultaneously perform ink supply amount adjustment (color tone adjustment) and registration adjustment of each color in a printing press.
Conventionally, not only an image is printed on a printing product printed by a printing press but also a color bar including color patches used to measure the densities of respective colors is printed in the top, bottom, or center margin of the printing product to extend laterally. The density of the printed color patch of each color is automatically measured by laterally moving an automatic scanning colorimeter. The density value of the measured color patch of each color is compared with a reference density value for this color to adjust the opening ratio of an ink fountain key of this color in accordance with the difference between these density values. Thus, the printing product is printed using a reference density value for each color. Note that instead of the density value, the color value may be measured. In this case, the printing product is printed using a reference color value for each color.
However, in measuring the color bar on the printed printing product using an automatic scanning colorimeter, the color bar must precisely be placed below the scanning path of the colorimeter. That is, the printing product must precisely be placed on a base on which the colorimeter is mounted to be movable in the X direction (the lateral direction; a direction perpendicular to the conveyance/printing direction) and the Y direction (the upward/downward direction; the conveyance/printing direction or circumferential direction regarding a cylinder), thus inflicting a heavy burden on the operator.
To solve this problem, a scanning apparatus which manipulates the color bar using a colorimeter including a line sensor with a upward/downward dimension larger than the width (upward/downward dimension) of the color bar is proposed, as disclosed in Japanese patent Laid-Open No. 8-043205 (literature 1). Literature 1 adopts a measurement scheme of detecting the central position of the color bar in the upward/downward direction using the line sensor to adjust the upward/downward position of the colorimeter in accordance with the detected central position. Using such a measurement scheme, the density value or color value of the color patch of each color in the color bar can precisely be measured as color matching data even if the printing product is not precisely placed on the base.
On the other hand, a register mark of each color used to adjust registration of this color is printed in the margin of the printing product printed by the printing press. According to Japanese Patent Laid-Open No. 62-99149, a cruciform register mark printed at a predetermined position for each color is captured by a camera to obtain the amount of positional shift of an image of each color based on a shift between a reference position and the position of the intersection point of the captured register mark for each color. The position of a plate cylinder of each color, which holds a printing plate of this color, and the position, in the skewing direction, of a transfer cylinder for printing paper conveyance, are adjusted as registration error amounts in accordance with the obtained amount of positional shift to match the position of the image of this color with the target position.
However, it is a conventional practice to provide the printing press with separate adjusting devices: an ink supply amount adjusting device which uses a color bar, and a registration adjusting device which uses register marks. The ink supply amount adjusting device includes a sensor for measuring color matching data of each patch, and a line sensor for detecting the upward/downward position of the color bar. On the other hand, the registration adjusting device includes a camera for detecting the positions of the register marks. Thus, the entire printing press entails a high cost. Also, the two devices require individual maintenance, thus inflicting a heavy burden on the operator.